Electric pick-up device



Oct. 22, 1929. H, ANDREWES 1,732,427

ELECTRIC PICK-UP DEVICE Filed July 28. 1923 c ll'z INVEHTOR Hum/reg lqha rcures HTTORNEY llll ' all)? Patented Oct. 22, 1929 UNITED STATESTPATENT OFFICE HUMFREY ANDRE'WES, OF LONDON, ENGLAND, ASSIGNOR OF ONE-HALF TO RADIO PAT- ENTS CORPORATION, OF NEW YORK, N. Y.

ELECTRIC PICK-UP DEVIOE Application filed July 28, 1928, Serial No. 296,059, and in Great Britain February 24, 1928.

This invention'broadly refers to an arrangement for translating mechanical movements into corresponding electrical variations and is more particularly directed to means for transforming the vibrations of the stylus of a phonograph into electrical variations for reproduction by a loudspeaker. Such devices have become known under the name of phonograph pick-up devices and are so constructed that they can be attached to an ordinary phonograph, in an easy manner. They present important advantages as,

compared to the direct reproduction by the stylus acting on the phonograph diaphragm,

i which primarily consists of a higher quality of the tones reproduced.

One object of this invention is to receive equal reproduction of the notes of the entire musical scale to be reproduced.

Another object of this invention is to provide combined electro-static and electromagnetic pick-up means in such a Way as .to

secure equal quality of reproduction of the entire band of frequencies to be translated.

The invention is more fully and specifical- 1y described by the following detailed disclosure taken in reference to the agcompany" ing drawings of which Fig. l is a sectional elevation of the pickup device constructed in accordance with my invention. A

a Fig. 2 is a front elevation of the device with the sound box cover, stylus, stylus lever, and part of the diaphragm removed.

Fig.3 is a diagram of connections.

In gramophone pickup and amplifying devices using the electro-magnetic principle, it has been found that the relationship between the response and frequency is not linear and usually there is a considerable falling ed in the response of the pick-up at the lower frequencies, whereas in those using the electrostatic principle there is a considerable falling off atthe' higher frequencies The invention consists of the arrangement of an electro-magnet, preferably annular in shape, having an annular rich as one pole and a centre boss as the other pole, between which poles is disposed a thin annular Winding, and a j a stretched steel diaphragm mounted in close in my U. S. application Serial No. 268,006,

filed April 6, 1928. In this combined arrangement the principles of the electro-magnetic and the electrostatic devices may be used simultaneously.

Referring first to Fig. 3, in the present cir- 0 cuit arrangements the electrostatic portion of the pick-up connected in the usual manner wherein the centre boss 1 of the electro-magnet 6 constitutes the back electrode and is connected to the positive pole 0f the polarizing battery 2 which is preferably variable and which is at the same time the'anode battery for the amplifying three-electrode tubes V and V arranged in resistance coupling connection. The magnetic diaphragm 3 is 0on I nected to the grid of an amplifying valve V and a coupling resistance 23' is connected between the said grid and the grid bias lead 11. The winding 5 on the electro-magnet 6 is connected through a battery 7 to the primary 8 of a step-up transformer 9 and the secondary 10 of the transformer is connected through the variable condenser 18 to the grid 4 at the minus grid bias lead 11 of the tube V A choke 12 is preferably connected in the lead 13 between the diaphragm 3 and the grid of the valve V and a resistance 14 is included in the circuit of the anode of the said valve, forming togetherwith a further lead resistance 15 and a condenser 21 the normal resistance coupling element between the tubes V and V 22 is a heating battery for the tubes and 23 is a grid biasing battery. 24 represents a loudspeaker inserted in the,

anode circuit of the last tube for reproduction of the sound vibrations of diaphragm3. 19 is a by-pass condenser bridging the part of resistance 20 inserted in the electrostatic pick-up circuit.

The action of the circuit is as follows Movements of the needle 16 actuated by variation of the grooves in the gramophone record cause-the stylus 17 to actuate the diaphragm 3 thereby varying the distance between the diaphragm and the boss 1 which constitutes the back electrode and thecentre pole piece. This movement has,two efiects: Firstly it causes a variation in capacity between the two electrodes represented by the pole-piece and the diaphragm, thereby producing an alternating E. M. F. across the resistance 23' connected between the grid and negative grid bias lead of the first amplifying tube V secondly the movement causes the flux in the electro-magnet 6, formed in the winding 5' and the pole piece 1 producing an alternating E. M. F. across the primary 8 of the transformer 9 which is transferred to the grid of the tube V through the variable condenser 18. The object of the introduction of the choke 12 in the lead of'the grid of tube V to the diaphragm 3 is. to prevent the shunting of the higher frequencies which are produced by two systems may the electro-ma manner the ob ect of the introduction of the etic system, and in a similar polarizing potential tapped from the potentiometer 20in the case of the electrostatic system and by the variable resistance 21 in the primary circuit of the electro-magnetic system. The actual values of the capacities of the variable condenser 18 and the choke 12 depend on the constants of the pick-up device itself.

Referring to the structural embodiment of the pick-up device shown by Figures 1 and 2, similar numerals refer to similar elements. 4 is the metallic tubular extension for connection with a horn or the like when using the device as an ordinary gramophone, which is connected to a terminal 24 serving for connectionto ground. 25 and 26 are terminals servingfor connection to the iron core 6 and the diaphragm 3, respectively and 27 and 28 are binding posts serving for connection with the terminals of the magnet coil 5. A

What I claim to be secured by Letters Pat- 'ent of the United States is;

luAn arrangement for translating me chanical movements into corresponding electrical variations comprising a flexible diaphragm subject .to said movements, an electric circuit producing a magnetic field associated with said diaphragm, a further .electric circuit including a capacity element, an electrode of said capacity element including said diaphragm, and means forcombining the electric variations occurring in said electric circuits due to the movement ,of dia phragms in a common translating device.

e varied by means of the diaphragm, means connecting said diaphragm to said stylus for imparting to it said J movements, an electric circuit linked with a magnetic field associated with said diaphragm, a further electric'circuit including a capacity element of which said diaphragm is a part, and means for combining the electric variations occurring in said electric ,circuits due to the movement of said diaphragm to a common translating device.

3. An arrangementfor translating the movements of the stylus of a phonograph into electrical variations, comprising a flexible diaphragm, means connecting said diaphragm to said stylus for imparting to it said movements, an electric circuit linked with a magnetic field associated with said diaphragm, a further electric circuit including a capacity element of which said diaphragm is a part, an electric discharge device having main electrodes and a control electrode, means to simultaneously apply varying. potential to said control electrode in accordance with electric variations in said electric circuits, and an electric reproducing device actuated. by the output circuit of said discharge device.

' 4. An arrangement for translating the movements of the stylus of a phonograph into electrical variations, comprising a flexible diaphragm of magnetic material subject'to said movements, pole pieces arranged opposite said diaphragm, an electric circuit including a winding arranged on said pole pieces, a further electric circuit including a capacity element constituted bysaid diaphragm and said pole pieces and means for combining electric varia ions in said electric circuits in a common translating device.

- 5. An arrangement for translatin the movementsof the stylus of a phonograp 1 into electrical variations, comprising a flexible diaphragm of'magnetic material subject to said movements, pole pieces arranged opposite said diaphragm, an electric circuit including a winding arranged on said pole pieces, a further electric circuit including a capacity element constituted by said diaphragm and said pole pieces, an electric discharge device having main electrodes and a control electrode, means to simultaneously apply varying potential to said control electrode in accordance with electric variations in said electric circuits, and an electric reproducing device actuated by the output circuit of said discharge device.

6. An arrangement as in claim 5, means for providing a variable polarizing voltage for 2. An arrangement for translating the electrical blocking means are provided in one movements of the stylus of a phonograph into circuit for the single resulting current for 65 electrical variations, comprising a flexible preventing variations of certain frequencies translated by one of the elements from being short-circuited by the other element.

8. An arrangement for translating mechanical movements into corresponding electrical variations comprising a flexible diaphragm subject to said movements, an electric circuit producing a magentic field associated with said diaphragm, a further electric circuit including a capacity element, an electrode of said capacity element including said diaphragm, means for combining the electric variations occurring in said. electric circuits due to the movement of diaphragms in a common translating device and means for varying the components of the single elec tric currents produced by said variations of said electric and magnetic field.

9. ln an arrangement for translating the mechanical movements of a stylus into corresponding electrical variations, comprising a moving member adapted for influencing an electrostatic and a magnetic field, means for transforming the variations of said electrostatic and said magnetic field into asingle electric current variation, and means for relatively varying the components of said electrostatic and said magnetic field producing said single electric current.

In testimony whereof I affix my signature.

HUMFREY ANDREWES. 

